This invention relates in general to weight measuring devices. More particularly, the invention relates to an onboard weight indicator for measuring the weight of a vehicle.
Onboard weight indicators such as shown in U.S. Pat. Nos. 3,648,790, 3,857,093, 3,955,636, and 4,623,029 are used to determine the weight of a load applied to a vehicle. Indicators of this type generally operate by measuring the deflection of the vehicle springs and then correlating the deflection with a known or calculated weight of the vehicle. A transducer is typically used to measure the spring deflection and a signal is then sent from the transducer to a suitable processor unit which calculates and displays the vehicle weight. These types of onboard weight indicators are particularly advantageous because they allow the vehicle load to be determined while the vehicle is being loaded and without requiring that the vehicle be positioned on a stationary scale.
Many of these conventional types of onboard weight indicators are mounted at opposite ends of each axle on the vehicle. Because of the costs associated with the transducers or other weight sensing portions of the weight indicators, a weight indicator was disclosed in U.S. Pat. No. 4,789,033 which allows a single transducer to be mounted between the tandem axles of a vehicle. This mounting arrangement allows the single transducer to be used to measure the load applied to a set of tandem axles. As a result, significant cost savings can be achieved in comparison to other weighing systems which require that a weight indicator be positioned at each end of every axle on the vehicle. Moreover, a system utilizing two transducers does not accurately account for certain types of movement. More specifically, such a system is not equipped to account for side to side movement of the vehicle, or loading of a vehicle on uneven ground. This is important because vehicles, especially trucks, encounter situations where they are carrying an uneven load, or are on an uneven road.
When using a single weight indicator to measure the deflection of tandem axles, it is important that the transducer be vertically oriented at a central position between the axles. When positioned in this manner, the transducer functions like a fulcrum and more accurately averages the movement experienced by both axles. Similarly, when one indicator is used on a single axle, the associated transducer should be centrally positioned between the ends of the axle to average the load applied to the axle. Often, however, the drive train or components of the vehicle frame interfere with the desired positioning of the transducer on tandem and single axle vehicles. The transducer must then be positioned off-center, with resulting inaccuracies in the measurement of a load applied to the axles. A need thus arose for an onboard weight indicator which allowed a single transducer to be mounted off-center and still maintain a more accurate averaging of the load applied to a single or tandem axle.
U.S. Pat. No. 5,522,468 disclosed an apparatus that addressed the above-identified need. The apparatus used an averaging arm that created a hole that monitored the average spring deflection in a suspension. The apparatus, however, used a somewhat complicated mechanical structure that spanned the distance between the two side rails of the truck, or spanned the distance between each of the axles of a tandem axle vehicle. Such a construction is complicated and relatively expensive to make and install properly on a vehicle. Moreover, such a construction often involved a corresponding movement of the transducer to the movement of the vehicle frame rail. Movements of this length can adversely affect the overall life of the transducer used.
Therefore, an apparatus is needed that overcomes the above drawbacks and disadvantages existing in the prior art. More specifically, an onboard weight indicator is needed that can accurately determine the weight of a vehicle and that is easily mounted to the vehicle without interference from the drive train thereof.